In the prior art, thermally expandable sheets in which a thermally expansive layer containing a thermally expandable material foaming and expanding according to the amount of heat absorbed is formed on one side of a base sheet are known. The thermally expansive layer can be distended in part or in whole by forming a photothermal conversion layer converting light to heat on the thermally expandable sheet and irradiating the photothermal conversion layer with light. Moreover, methods of forming a shaped object having a stereoscopically uneven surface on the thermally expandable sheet by changing the shape of the photothermal conversion layer are also known (for example, see Patent Literature Unexamined Japanese Patent Application Kokai Publication Nos. S64-28660 and 2001-150812).
In some thermally expandable sheets, the thermally expandable material (for example, thermally expandable microcapsules) aggregates on the surface while the thermally expansive layer foams. This particularly notably occurs when the content of the thermally expandable material is increased. As the thermally expandable material aggregates, the thermally expansive layer has an uneven surface. Consequently, problems are that the surface becomes rough, the sheet surface is deteriorated in smoothness, and the sheet surface easily peels off when rubbed.
Therefore, there is a demand for a thermally expandable sheet comprising a surface excellent in smoothness and rub resistance even after the thermally expansive layer is distended.
The present disclosure is made with the view of the above situation and an objective of the disclosure is to provide a thermally expandable sheet comprising a surface excellent in smoothness and rub resistance even after the thermally expansive layer is distended and a method of producing the thermally expandable sheet.